There is a need to be able to create and control patterns in cement and plaster or gypsum based materials in both precast products and cast-on-site pieces. At present, the ability to create and control patterning in cement is extremely limited. Most commonly, if an attractive stone appearance is desired on a cement based material it is usually achieved by covering with a veneer of granite or marble.
Some of the disadvantages of marbles and granites which can be solved by this invention are lot-to-lot variation in color and pattern, limits in size due to costs of handling and transportation, difficulty in showing continuous patterns of marble veins, and cost. With regard to the problem of lot-to-lot variation and showing a continuous veining pattern, since marble and granite are natural materials, there is no control over the consistency of color and pattern from one piece to the next. It is often necessary to compare and match many different pieces to obtain a few which are sufficiently similar to be used to create a uniform appearance on a facing. As for size and cost, it is not practical to use marble in pieces larger than approximately four feet by eight feet.
The prior art is replete with methods to produce color and patterns in cast materials to simulate a natural stone appearance, such as marble or granite. However, in most instances there is little or no control over the pattern or its reproducibility. Furthermore, few, if any, of the prior art methods are readily adaptable to automation for consistent production of matching articles.
For example, U.S. Pat. No. 27,022, Lamb, discloses a method for manufacturing artificial marble in which balls of cement are mixed up to a consistency of paste and partially coated with dry paint. The balls are then placed in a mold and compressed causing the moisture within each ball to penetrate the dry material and consolidate into a single mass. The dry paint then appears as streaks on the surface of the article produced. This method is time consuming and requires precision on the part of the practitioner to achieve any degree of consistency from one piece to the next. Nor is it readily adaptable to an automated process.
U.S. Pat. No. 106,263, Frear, discloses the manufacture of artificial marble in which a solution of zinc sulphate, zinc chloride, sugar of lead, alum or salt is combined with a mixture of cement and silex to form a pasty mass having the consistency of mortar which is then cast in molds. By adding suitable colorants to the composition while it is in its plastic state or to the solution with which it is moistened, imitations of marble are obtained. Clearly, colorants added to the plastic mass would require some mixing to achieve a marble-like pattern, similar to the process used in mixing the two colors of a marble cake batter.
U.S. Pat. No. 134,300, Mellen, discloses a method of manufacturing artificial marble in which individual batches of cement of particular colors are prepared in separate vessels having small spouts. These are then individually poured into a mold in small streams in imitation of the veins of marble and the area between these streams filled in with cement of another color. Air is then blown across the mold to cause the colors to flow and mingle together until the desired effect is achieved. For finer veins, threads are dipped in colors and laid in the mold to be pulled through the cement after it is poured in. As with the Lamb patent, this method requires a degree of care and skill on the part of the practitioner to achieve any degree of consistency of pattern from one piece to the next.
U.S. Pat. No. 635,005, Summers, discloses artificial marble which is manufactured by mixing together lime-water and silicate of soda and adding a cement until it is fully incorporated. Pigments mixed with dry cement are then added and agitated into the mixture by stirring with a suitable tool. This mixture is then poured into a mold and allowed to set. This method, whereby pigment is merely stirred into a base mixture is the classic "marble cake" method and is very difficult to control from one casting to the next.
U.S. Pat. No. 704,621, Czermak, discloses a process of manufacturing artificial marble in which cement, or the like, is spread upon a smooth surface and allowed to partially set to form a slab. A liquid mass of mortar, or similar substance, having a color corresponding to the color of the veins desired is poured over the slab which is then cracked through its entire thickness with a suitable instrument to slightly displace its component parts. The liquid mass enters the cracks and produces the artificial veins which penetrate from face to face of the slab. Since the shape and direction of cracking in the slab is dependent in part on the application of the instrument and in part on the structure of the slab itself, it is unlikely that a great degree of consistency in pattern can be achieved from one piece to the next using this method. In addition, since cracking of the slab disrupts the internal structure, this method has the added effect of weakening the slab.
U.S. Pat. No. 928,061, Mitats, discloses an artificial marble which comprises portland cement, marble dust, sand, a colorant and water which are mixed together and compressed in a mold. In this method, it is believed that the resulting product will be substantially of one color with the marble dust providing any variation which may be present.
U.S. Pat. No. 2,280,488, Jenkins, et al., discloses a method and apparatus for making a stone like unit in which batches of colored concrete are premixed and added in layers to a blending box. A mixing grid is drawn vertically through the layers at least once to mix them in a variation of the "marble cake" method of the Summers patent. After the layers are blended in this manner, the mixture is poured from the box into a mold.
U.S. Pat. No. 5,248,338, Price discloses a colored marble concrete and a method of producing the same wherein a master mix of concrete of a desired primary color is prepared. Secondary or accent colors are added to the surface of the master mix within a container, such as a bucket, and are stirred to create a swirl pattern in the colors. The stirred mix is then poured into a mold. As with Summers, thiss the classic "marble cake" method which is difficult to control from one casting to the next.
In contrast to the prior art, the present invention provides a method whereby color and pattern can be controlled and replicated across many castings to provide uniformity of color and pattern as well as, where desired, continuous veining from one piece to the next. The method of this invention is adaptable to any size of casting, both on and off-site, and to most means for transferring casting mixtures to a mold as well as to automated production systems for producing substantially consistent and identical articles.